GB378983A - Apparatus for measuring magnetically the thickness of iron plates and the like - Google Patents

Abstract

378,983. Gauging apparatus. MOORE, H., WILLIAMSON, G., and BRITISH SCIENTIFIC INSTRUMENT RESEARCH ASSOCIATION, 26, Russell Square, London. Feb. 17, 1932, No. 11403. [Class 106 (ii).] Measurement of the thickness of plates of magnetic material accessible on one side only, such as boiler plates, ships' hulls, &c. is made from measurement of the steady flux produced therein by a permanent or direct-current electromagnet. In Fig. 2 an electromagnet having an energizing winding g and polepieces b is placed against the plate, and the flux produced therein measured by the reduction in the reading of a steady flux measuring instrument r placed in an alternative flux-path of the magnet. The instrument r may be a bismuth spiral included in a resistance measuring circuit, or a torsion magnetometer, Fig. 3 (known per se) having magnets s supported on a spindle, pivoted in a brass case v, and controlled by a spiral spring z carried by a torsion head w. The instrument r is calibrated to read directly in thickness by previous observation on plates of the same material and known thickness. In the modification of Fig. 5, coils a<1>, b<1> are mounted at right-angles on a common axis furnished with a pointer h<1>, suitably connected to a direct-current supply h<1>, i, and placed respectively in the field of two electromagnets energized from the same supply so as to render readings independent of the supply voltage. One of the magnets has polepieces b for placing against the plate under test, whilst the other magnet (not shown) is screened therefrom. In a simplified and portable form, permanent magnets are used, and the current supplied from a dry-cell or accumulator.